When winding strips of web materials onto spools, a common practice has been to attach the lead end of the strip to the core of the spool by means such as a strip of tape between the lead end and the core or by means of a mechanical engagement between the lead end and the core. For many types of web materials, contact with the strip of tape or deformations in the web due to the mechanical engagement can cause the first few convolutions of the web material to be deformed slightly and to exhibit pressure marks. These marks may be so prominent as to be unsightly for some web materials, but may also be quite subtle in appearance. Where the web material is photographic film, such pressure marks have long been known to cause defects in the images produced in the film over the first few convolutions, an unacceptable situation for photographers. Contact with the tape can also cause abrasion marks and transfer of dirt from the tape to the photographic film, each of which can lead to irregularities in the processed film.
Various techniques have been tried to space the second convolution of a strip of web material from the underlying strip of tape or deformation of the first convolution, in order to reduce pressure marking, abrasion and transfer of dirt. U.S. Pat. No. 1,672,510 shows a spindle for winding a strip of gelatin in which the center of the spindle has a reduced diameter portion to permit winding of a narrow leader for the strip without creating a bulge in the successive convolutions of the strip. U.S. Pat. No. 1,930,144 shows a spool for photographic film in which the ends of the core of the spool are provided with axially extending shoulders between which a reduced diameter portion is formed for receiving at least a portion of the first convolution of film.
While spindles or spools of these general types have been widely used, the advent of more pressure sensitive web materials, such as certain state of the art photographic films, has brought a need for spools or lead end geometries, or both, which are configured to further minimize any tendency to produce pressure marks. This is because the light sensitive emulsions used in modern photographic films are susceptible to pressure marking due to smaller deformations and slighter pressures than could be withstood by previous films.